Distributed Feedback (DFB) lasers are finding increasing importance in optical fiber communications systems since they provide a stable source of light at a narrow line width. Such lasers are characterized by the presence of a periodic variation of the laser structure usually referred to as the "grating". These gratings can be distributed in the active region of the laser or can be formed outside the boundaries of the active region. The gratings usually take the form of a periodic variation in the index of refraction of the structure, resulting in a "refractive index coupled" laser or a "loss coupled laser", depending upon the bandgap of the layer including the grating. It is generally believed that the loss coupled lasers are more advantageous due to reduced spatial hole burning, reduced sensitivity to external reflections, and other factors.
In a typical loss coupled laser, the grating is formed by materials of different bandgaps. (See, e.g., U.S. Pat. No. 5,506,859 issued to Ackerman, et al.) While acceptable, such designs require a fair degree of control in manufacture due to the changing of the composition of the materials.